Outwardly-looking radar, infrared, and/or visible-light sensors built into vehicles such as aircraft or missiles are usually protected by a covering termed a dome or radome. The dome serves as a window that transmits the radiation sensed by the sensor. It also acts as a structural element that protects the sensor and carries aero-dynamic loadings. In many cases, the dome protects a forward-looking sensor, so that the dome must bear large aerostructural loadings.
In one embodiment, an infrared seeker system for missile design generally employs as the dome a protective non-opaque surface to protect its inherently delicate components. Typical applications for this protective surface are semi-spherical or semi-aspherical (conformed) ceramic domes. One popular material for missile applications in the infrared wavelength band is sapphire (a form of Al2O3). These sapphire domes must be located to the missile body by one or more attachment mechanisms.
A common practice for these attachment mechanisms is kinematic mechanical clamps or locating devices combined with high temperature silicon glue. Failure in these joints can occur due to missile flight dynamics, causing thermal and stress conditions exceeding the operational strength of the joint. Over the last few years, Raytheon engineers have devised techniques and processes to replace the silicon joints with brazed sapphire dome assemblies; see, e.g., U.S. Pat. No. 5,758,845, entitled “VEHICLE HAVING A CERAMIC RADOME WITH A COMPLIANT, DISENGAGEABLE ATTACHMENT”, issued on Jun. 2, 1998, to Wayne Sunne et al; U.S. Pat. No. 5,884,864, entitled “VEHICLE HAVING A CERAMIC RADOME AFFIXED THERETO BY A COMPLIANT METALLIC TRANSITION ELEMENT”, issued on Mar. 23, 1999, to Wayne Sunne et al; U.S. Pat. No. 5,941,479, entitled “VEHICLE HAVING A CERAMIC RADOME AFFIXED THERETO BY A COMPLIANT METALLIC “T”-FLEXURE ELEMENT”, issued on Aug. 24, 1999, to Wayne L. Sunne et al; U.S. Pat. No. 6,123,026, entitled “SYSTEM AND METHOD FOR INCREASING THE DURABILITY OF A SAPPHIRE WINDOW IN HIGH STRESS ENVIRONMENTS”, issued on Sep. 26, 2000, to James H. Gottlieb; U.S. Pat. No. 6,241,184, entitled “VEHICLE HAVING A CERAMIC RADOME JOINED THERETO BY AN ACTIVELY BRAZED COMPLIANT METALLIC TRANSITION ELEMENT”, issued on Jun. 5, 2001, to Wayne Sunne et al. The foregoing patents are all assigned to the same assignee as the present application. Brazed sapphire dome assemblies have out-performed earlier state-of-the-art assemblies.
Nevertheless, improvements are continually sought to further reduce stresses related to the different coefficients of thermal expansion in the sapphire (dome)/niobium (transition)/titanium (body) connection.